title: Effects of Mesoporous Silica Coating and Post-Synthetic Treatment on the Transverse Relaxivity of Iron Oxide Nanoparticles.
abstract: Mesoporous silica nanoparticles have the capacity to load and deliver therapeutic cargo and incorporate imaging modalities, making them prominent candidates for theranostic devices. One of the most widespread imaging agents utilized in this and other theranostic platforms is nanoscale superparamagnetic iron oxide. Although several core-shell magnetic mesoporous silica nanoparticles presented in the literature have provided highT2contrastin vitroandin vivo, there is ambiguity surrounding which parameters lead to enhanced contrast. Additionally, there is a need to understand the behavior of these imaging agents over time in biologically relevant environments. Herein, we present a systematic analysis of how the transverse relaxivity (r2) of magnetic mesoporous silica nanoparticles is influenced by nanoparticle diameter, iron oxide nanoparticle core synthesis, and the use of a hydrothermal treatment. This work demonstrates that samples which did not undergo a hydrothermal treatment experienced a drop inr2(75% of originalr2within 8 days of water storage), while samples with hydrothermal treatment maintained roughly the samer2for over 30 days in water. Our results suggest that iron oxide oxidation is the cause of ther2loss, and this oxidation can be prevented both during synthesis and storage by the use of deoxygenated conditions during nanoparticle synthesis. The hydrothermal treatment also provides colloidal stability, even in acidic and highly salted solutions, and a resistance against acid degradation of the iron oxide nanoparticle core. The results of this study show the promise of multifunctional mesoporous silica nanoparticles but will also likely inspire further investigation into multiples types of theranostic devices, taking into consideration their behavior over time and in relevant biological environments.
authors.affiliation: Department of Chemistry, University of Minnesota, 207 Pleasant Street Southeast, Minneapolis, Minnesota 55455, United States.
authors.forename: Katie R
authors.initials: KR
authors.lastname: Hurley
authors.forename: Yu-Shen
authors.initials: YS
authors.lastname: Lin
authors.forename: Jinjin
authors.initials: J
authors.lastname: Zhang
authors.forename: Sam M
authors.initials: SM
authors.lastname: Egger
authors.forename: Christy L
authors.initials: CL
authors.lastname: Haynes
keywords: hydrothermal treatment; iron oxide; mesoporous silica; nanoparticles; transverse relaxivity